High-pressure gas discharge lamp containing germanium and selenium

ABSTRACT

A high-pressure gas discharge lamp provided with a gas filling which comprises at least 10 7 gram atoms of germanium per cubic cm of the discharge vessel and selenium. The selenium-germanium ratio has a value of between 0.5 and 4. Furthermore the gas filling may comprise tin and a halogen in which the seleniumhalogen ratio is chosen between 0.02 and 4. In addition to the said elements the lamp preferably includes a starter gas (rare gas) and a buffer gas (mercury). The lamp emits the continuous molecular radiation of germanium selenide and a very satisfactory colour rendition is possible in a wide range of colour temperature.

United States Patent Van Eijl et a1.

1 1 Oct. 9, 1973 HIGH-PRESSURE GAS DISCHARGE LAMP CONTAINING GERMANIUM AND SELENIUM Inventors: Antonie Peter Lambertus Van Eijl;

Alexander Gray Jack; Harry Nienhuis, all of Emmasingel, Eindhoven, Netherlands Assignee: U.S. Philips Corporation, New

York, N.Y.

Filed: May 24, 1972 Appl. No.: 256,578

Foreign Application Priority Data June 2, 1971 Netherlands 7107535 US. Cl 313/184, 313/227, 313/229 Int. Cl. H0lj 61/12 Field of Search 313/229, 184, 225,

References Cited UNITED STATES PATENTS 2/1966 Reiling 313 225 x 3,521,110 7/1970 Johnson 313/229 X Primary Examiner-Palmer C Demeo AttorneyFrank R. Trifari 57 ABSTRACT A -Pres e s ed s2 eselamppro w t a gas lilling which comprises at least IO granTitoms of germanium per cubic cm of the discharge vessel and selenium. The selenium-germanium ratio has a value of between 0.5 and 4. Furthermore the gas filling may comprise tin and a halogen in which the seleniumhalogen ratio is chosen between 0.02 and 4. In addition to the said elements the lamp preferably includes a starter gas (rare gas) and a buffer gas (mercury). The lamp emits the continuous molecular radiation of germanium selenide and a very satisfactory colour rendition is possible in a wide range of colour temperature 8 Claims, 3 Drawing Figures PAIENTED 0B1 3. 764. 843

sum 2 or 2 Mnm) Fig. 2

Fig.3

HIGH-PRESSURE GAS DISCHARGE LAMP CONTAINING GERMANIUM AND SELENIUM The invention relates to a high-pressure gas discharge lamp having a light-transmitting discharge vessel provided with a gas filling-in which the discharge takes place.

A lamp of this kind which has been known for a long time and is used on a large scale is the high-pressure mercury vapour discharge lamp. A drawback of this lamp is that it has less satisfactory colour rendition properties and is therefore less suitable for general illumination purposes in which a satisfactory rendition of colours is required. 1

The addition of metal halides, particularly metal iodides to the filling in high-pressure gas discharge lamps, particularly high-pressure mercury vapour discharge lamps, provides a considerable improvement of colour rendition in many cases and also of the radiation efficiency of the lamps (see U.S. Pat. No. 3,234,421). Said Patent Specification describes, for example, a lamp which in addition to a rare gas and mercury contains theiodides of sodium, thallium and indium. These metals emit their characteristic radiation during operation of the lamp while the mercy spectrum is suppressed so that a lamp is obtained which has a much better colour rendition than the lamps containing mercury only. The spectrum of the emitted radiation of these iodidecontaining lamps is, however, predominantly constituted by spectral lines and thus deviates considerably from the continous spectrum of a black radiator or of natural daylight. lf very stringent requirements are im' posed on the rendition of colours, a continuous spectrum of the radiation emitted by the lamp is necessary.

A high-pressure gas discharge lamp containing tim bromide and/or tin iodide is known from the Netherlands Pat. application No. 6610396. This lamp emits radiation originating from the .tin halide molecules. Thismolecular radiation has a continuous spectral distribution of such a shape that a very satisfactory colour rendition can be obtained. A drawback of the known lamps which generally contain both tin bromide and tin iodide is that with these lamps colour temperatures of the emitted radiation can be achieved which are located in a relatively limited region namely between approximately 4,000 and 6,000 K.

A high-pressure gas discharge lamp which emits molecular radiation having a continuous spectrum is furthermore known from German Pat. application No. 2,023,770. This lamp contains tin chloride and furthermore tin, either as a metal or as tin iodide. It is stated that the use of tinchloride generally yields higher radiation efficiencies than the use of tin bromide and tin iodide. A drawback of this known lamp is, however, that the presence of the aggressive chlorine may give rise to serious chemical attack of the electrodes.

The object of the invention is to provide a highpressure gas discharge lamp which contains new molecular radiators. A further object of the invention is to provide a lamp of this kind which does not have the above-mentioned drawbacks of the known lamps or has these drawbacks to a limited extent only and which has very satisfactory colour rendition properties in a large region of colour temperatures.

A high-pressure gas discharge lamp according to the invention has a light-transmitting discharge vessel provided with a gas filling in which the discharge takes place and is characterized in that the'filling comprises at least gram atoms of germanium per cubic centimetre of contents of the discharge vessel and selenium, the ratio between the numbers of atoms of selenium and germanium being between 0.5 and 4.

A lamp according to the invention comprises germanium selenide which is introduced assuch or in the form of the composite elements into the lamp. Investigations which have led to the invention have shown that germanium selenide is an efficient molecular radiator whose emitted radiation has a continuous spectral distribution at a maximum of between 360 and 380 nm. The quantity of germanium in a lamp according to the invention is to be at least 10 gram atoms per cubic cm of contents of the discharge vessel. In fact, when less than this quantity is used an insufficient effect of the 1 addition of germanium selenide is obtained and light outputs which are too low'in practice are obtained. For practical uses the quantity of germanium is chosen to be not more than 10 gram atoms per cubic cm because more germanium does not provide additional advantages and only gives rise to a quantity of unevaporated germanium and/or germanium selenide during operation of the lamp. The ratio between the number of atoms of selenium and germanium may deviate from the stoichiometric value 1 which applies to the compound GeSe. This ratio is, however, to be chosen between the values 0.5 and 4 because for values of more than 4 a too large quantity of free selenium is present in the lamp which may give rise to the production of ultraviolet radiation which is unwanted for many uses, and because for values of less than 0.5 free germanium may be deposited on the wall of the discharge vessel which may detrimentally influence the light output of the lamp.

A special advantage of a lamp according to the invention is that the discharge is stable even at high values of the concentration of germanium selenide present in vapour form during operation of the lamp. in the known tin halide containing lamps disturbing instabilities of the discharge occur above given tin halide concentrations. In a lamp according to the invention it is possible to use an excess of germanium selenide so that the vapour pressure of germanium selenide is only limited by the temperature of the coldest spot in the lamp.

A lamp according to the invention which comprises germanium selenide only may advantageously be used for many applications, for example, in photo-chemical processes. However, this lamp is less suitable for general illumination purposes because the emitted radiation is too blue and has a very high colour temperature 12,000 K).

The colour temperature of a lamp according to the invention may, however, assume values which are very desirable for general illumination purposes if in addition to germanium and selenium other radiators are added to the filling of the lamp, which radiators exhibit a considerable emission in the red part of the visible spectrum. A very satisfactory colour rendition can be achieved with a lamp of this kind.

For this purpose tin and one or more of the halogens are preferably added in addition to germanium and selenium to the filling of a lamp. The ratio between the numbers of atoms of halogen and tin must then be not more than 4 because otherwise too much free halogen is present in the lamp which gives rise to instabilities of the discharge. In practice this ratio is chosen to be not less than 0.5 because below this value a too large quantity of free tin is present which does not contribute to the light emission. The ratio between the numbers of atoms of selenium and halogen is chosen to be between 0.02 and 4. At values of this ratio of less than 0.02 the contribution of germanium selenide to the emitted radiation is too small while for values of more than 4 the colour temperature of the emitted radiation is too high for general illumination purposes. For seleniumhalogen ratios in the above-mentioned region it is possible to manufacture lamps whose colour temperature is located in the very wide range of approximately 4,000 to approximately 12,000 K.

Furthermore a starter gas and a buffer gas is preferably applied in known manner to the filling of a lamp according to the invention. The starter gas which serves to promote the ignition of the lamp generally consists of a rare gas or a mixture of rare gases having a pressure of between, for example, 1 and 100 Torr (at room temperature). The buffer gas serves to increase the overall pressure in the discharge lamp and to increase the arc voltage so that a larger quantity of energy can be dissipated in the lamp. Mercury in a quantity of between 2.5- and 210 gram atoms per cubic cm of contents of the discharge vessel is preferably used as a buffer gas.

Lamps according to the invention which in addition to germanium and selenium also contain tin and a halogen and in which the halogen is iodine and/or bromide are preferred. In fact, tin iodide and tin bromide emit molecular radiation whose contribution in the red part of the spectrum is larger than that of tin chloride so that when using tin iodide and/or tin bromide for general illumination purposes the optimum implementation of the germanium selenide spectrum is obtained. Furthermore iodine and bromide have the advantage that they are less aggressive than chorine so that electrode attack and the like are limited to a minimum.

Optimum results are obtained with lamps according to the invention in which the ratio between the numbers of atoms of halogen and tin is between 1.5 and 2.5 and the ratio between the numbers of atoms of selenium and germanium is between 0.8 and 1.2. At these ratios the formation of free tin and free germanium deposited on the wall of the lamp and on the electrodes is limited to a minimum and a too large excess of free halogen and free selenium is also prevented.

In a particularly advantageous embodiment of a lamp according to the invention the quantity of germanium is between 510 and 210 gram atoms per cubic cm of contents of the discharge vessel and the ratio between the numbers of atoms of selenium and halogen is between 0.05 and 2. In fact, a very satisfactory colour rendition is achieved with these lamps at the colour temperature values of more than 5,000 K which are very much desirable for practical uses. Lamps having such a relatively high colour temperature can be used to great advantage for scene lighting for colour television recordings, especially in those cases where the lamps are used together with daylight.

The invention will now be further described in detail with reference to a drawing and a number of examples and measurements.

In the drawing FIG. 1 shows an embodiment of-a lamp according to the invention.

FIGS. 2 and 3 graphically show the spectral distribution of the emitted radiation of two lamps according to the invention.

In FIG. 1, l is the quartz glass discharge vessel of a high-pressure gas discharge lamp according to the invention. Pinches 2 and 3 in which current supply elements 4 and 5 have been sealed are formed at both ends of the discharge vessel 1. These current supply elements are connected within the discharge vessel to tungsten electrodes 6 and 7 between which the discharge takes place during operation. The discharge vessel 1 is placed in an outer envelope 8, for example, of hard glass one end of which has a pinch 9 through which current supply wires 10 and 11 are passed in a vacuum-tight manner. The current supply wires 10 and 11 are connected to the current supply elements 4 and 5 and also serve as supporting terminals for the discharge vessel. The discharge vessel 1 has an internal diameter of 15.5 mms and a content of 7.5 cubic cm. The distance between the electrodes is 41 mms. The lamp is suitable for a power of 400 W.

EXAMPLE 1 spectral distribution of this lamp according to the invention, which in addition to mercury and argon comprises germanium and selenium only, is found to consist of a continum which extends throughout the visible part of the spectrum up to the ultraviolet part of the spectrum with a maximum at approximately 360-380 nm. In addition to this continuum originating from germanium selenide molecules, mercury lines and germanium lines are also present in the spectral distribution.

EXAMPLES 2, 3 and 4 Three lamps (to be denoted by characters A, B and C, respectively) having a construction as shown in FIG. 1 are provided with the following filling: 1.5 mg of tin, 5.7 mg of mercury iodiode (I-IgI 22 mg of mercury and argon up to a pressure of 20 Torr. Furthermore the lamps contain germanium selenide (GeSe) in the quantities mentioned below:

Lamp A 1.0 mg

Lamp B 3.0 mg

Lamp C 5.0 mg

The colour temperature T, and the light output LO of these lamps which consume a power of 400 W during operation have been measured. The measurements are summarised in thefollowing table.

TABLE lamp ratio Sell T. in K L0 in Im/W A 0.26 6830 44 B 0.78 10250 40 C 1.30 1l000 32 The measurements show that higher colour temperatures are achieved with increasing values of the ratios between the numbers of atoms of selenium and halogen (Se/I).

EXAMPLE 5 The spectral distribution of the radiation emitted by this lamp is shown in a graph in FIG. 3. This embodiment of a lamp according to the invention is very suitable for general illumination purposes in those cases in which in addition to a perfect colour rendition a high colour temperature is required.

What is claimed is:

l. A high-pressure gas discharge lamp comprising:

a light transmitting discharge vessel having at least a pair of electrodes secured thereto for exciting the V lamp, said vessel provided with a gas filling in which the discharge takes place, said gas filling including at least 10' gram atoms of germanium per cubic centimeter of contents of the discharge vessel and selenium, the ratio between the numbers of atoms of selenium and germanium being between 0.5 and 4.

2. A high-pressure gas discharge lamp as claimed in claim 1, wherein the filling further comprises tin and at least one halogen, in which the ratio between the number of atoms of halogen and tin is not more than 4 and in which the ratio between the numbers of atoms of selenium and halogen is between 0.02 and 4.

3. A high-pressure gas discharge lamp as claimed in claim 2 wherein the halogen is iodine.

4. A high-pressure gas discharge lamp as claimed in claim 2 wherein the ratio between the numbers of atoms of halogen and tin is between 1.5 and 2.5 and that the ratio between the numbers of atoms of selenium and germanium is between 0.8 and 1.2.

5. A high-pressure gas discharge lamp as claimed in claim 2 wherein the quantity of germanium is between 5 X 10* and 2 X 10' gram atoms per cubic cm of contents of the discharge vessel, and that the ratio between the numbers of atoms of selenium and halogen is between 0.05 and 2.

6. A high-pressure gas discharge lamp as claimed in claim 2 wherein the halogen is bromine.

7. A high-pressure gas discharge lamp is claimed in claim 2 wherein the halogens are iodine and bromine.

8. A high-pressure gas discharge lamp as claimed in claim 1 wherein the filling comprises a starter gas and furthermore between 2.5 X 10 and 2 X 10 gram atoms of mercury per cubic cm of contents of the discharge vessel as a buffer gas. 

2. A high-pressure gas discharge lamp as claimed in claim 1, wherein the filling further comprises tin and at least one halogen, in which the ratio between the number of atoms of halogen and tin is not more than 4 and in which the ratio between the numbers of atoms of selenium and halogen is between 0.02 and
 4. 3. A high-pressure gas discharge lamp as claimed in claim 2 wherein the halogen is iodine.
 4. A high-pressure gas discharge lamp as claimed in claim 2 wherein the ratio between the numbers of atoms of halogen and tin is between 1.5 and 2.5 and that the ratio between the numbers of atoms of selenium and germanium is between 0.8 and 1.2.
 4. IN ADDITION TO THE SAID ELEMENTS THE LAMP PREFERABLY INCLUDES A STARTER GAS(RARE GAS)AND A BUFFER GAS(MERCURY). THE LAMP EMITS THE CONTINUOUS MOLECULAR RADIATION OF GERMANIUM SELENIDE AND A VERY SATISFACTORY COLOUR RENDITION IS POSSIBLE IN A WIDE RANGE OF COLOUR TEMPERATURE.
 5. A high-pressure gas discharge lamp as claimed in claim 2 wherein the quantity of germanium is between 5 X 10 7 and 2 X 10 5 gram atoms per cubic cm of contents of the discharge vessel, and that the ratio between the numbers of atoms of selenium and halogen is between 0.05 and
 2. 6. A high-pressure gas discharge lamp as claimed in claim 2 wherein the halogen is bromine.
 7. A high-pressure gas discharge lamp is claimed in claim 2 wherein the halogens are iodine and bromine.
 8. A high-pressure gas discharge lamp as claimed in claim 1 wherein the filling comprises a starter gas and furthermore between 2.5 X 10 6 and 2 X 10 4 gram atoms of mercury per cubic cm of contents of the discharge vessel as a buffer gas. 